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Vol. 46, No. 2, March 1, 2011

can be catasrophic for people in passen er veh icles that run into the backs of heavy trucks. The steel guardsbacks of big rigs are supposed to stop smaller vefrom s liding underneath trailers, but a new Institut

ysis of real-world crashes indicates that too ofteguards intended to prevent underride buckle or break away from their trailers with deadly consequences. To understand how this happens, the Institute ran a seof crash tests and discovered that guards meeting fsafety standards can fail in relatively low-speed crBased on th is research , the Institute is petitioning tional Highway Trafc Safety Administration (NHT

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2 Status Repo rt, Vol. 46, No. 2, March 1, 2011

in a vehicle that e arns to p marks in frontalcrash tests, but if the trucks underrideguard fails or isnt there at all yourchances of walking away from even a rela-tively low-speed cr ash a rent good .

NHTSA has estimated that about 423 peo-ple in passenger vehicles die each yearwhen th eir vehicles s trike th e backs of largetrucks. More than 5,000 passenger vehicleoccupant s are injured.

Pinpointing precisely how many large truckunderride deaths occur each year is difcultbecause federal databases th at track crashesare known to underestimate the incidence of underride. A 1997 Institute study estimatedthat under ride occurred in half of fatal crash-es b etween large trucks and passenger vehi-cles (seeStatus Report,Feb. 15, 1997).

Real-world crashes: To identify crashpattern s leading to rear un derride of heavytrucks and semi-trailers with and withoutguards, Institute research ers an alyzed caseles from the Large Truck Crash Causation

Study, a federal database of roughly 1,000real-world crashes in 2001-03. Underridewas a common outcome of the 115 crashesinvolving a passenger vehicle striking theback of a heavy truck or semi-trailer. Only 22percent of the crashescontinues on p. 4)

require underride guards that are strongenough to remain in place during a crashand to broad en rules to mandate guards formore large trucks and trailers.

Any crash between a large truck and a pas -

senger vehicle is a r isky event. In 2009, 70 per-cent of the 3,163 people who died in largetruck crashes were occupants of cars or otherpassenger vehicles. Underride makes deathor s erious injury more likely since the upperpart of the passenger vehicles occupant com-partment typically crushes as the truck bodyintrudes into the vehicle safety cage. Rearguards are the main countermeas ure for re-ducing underride deaths and injuries.

A 2009 Institute study and a similar oneby NHTSA examined why people s till die incrashes despite tremendous advances inpass enger vehicle occupan t protection. Un-derride cras hes with large trucks were iden-tied as among the most deadly (seeStatus Report March 7, 2009, and Feb. 6, 2010; onthe web at iihs.org).

Cars front-end structures are designedto manage a tremendous amount of crashenergy in a way that minimizes injuries fortheir occupants, says Adrian Lund, Insti-tute president. Hitting the back of a largetruck is a game cha nger. You might b e riding

10%

20%

30%

none negligible slight moderate severe catastrophic

severe catastrophic

n e g l i g i b l e

s l i g h t

m o d e r a t e

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UNDERRIDE AND INJURY SEVERITY IN 115 REAL-WORLD CRASHE

UnknownFatalSeriousMinor

THIS IS HOW A MALIBU LOOKS after a40 mph frontal crash with another car.The front structure managed the crashenergy to preserve survival spacein the occupant compartment. TheMalibu is aT P S FETYPI K

THIS IS HOW A MALIBU LOOKS after a35 mph crash into a trailer with a weakunderride guard. The cars front crumplezone never got the chance to do its jobbecause the guard fail ed. In a real crashpeople could have been decapitated.

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Status Report, Vol. 46, No. 2, March 1, 2011 3

REGULATORS SLOW TO ACT ON UPGRAD The Institute has studied the underride crash problem

for more than 30 years, including mid-1970s crashtests demonstrating how then-current guards wereineffective in preventing underride (seeStatus Report , March 29, 1977; on the web at iihs.org).

Federal rules put in place in 1953 requiredinterstate carriers to have rear underride guardsmeeting specications for ground clearance,setback, and width, but not strength, energyabsorption, or attachment methods.

The National Highway Safety Bureau, predecessorto the National Highway Trafc Safety Administratio(NHTSA), indicated in 1967 that it would develop new standard, but the agency abandoned the effortin 1971 even though the National TransportationSafety Board recommended that energy-absorbingunderride and override barriers on trucks, trailers,and buses be required.

In 1977 the Institute demonstrated that a 30 mphcrash of a Chevrolet Chevette into a tractor-trailerwith a rear guard meeting the US rule resulted insevere damage to the cars occupant compartment.The Institute petitioned NHTSA for a new standard.

It took the agency nearly 20 years to publish newrules. The upgrade took effect in 1998 and resulted inlower and wider underride guards under Federal MotoVehicle Safety Standard 224. Another standard, Federal Motor Vehicle Safety Standard 223, introducedquasi-static test requirements specifying minimumlevels of strength and energy absorption (see tatus Report , March 2, 1996). The standards cover newtrailers but exempt many types of heavy trucksused in everyday commerce including straighttrucks, wheels-back trucks, and special purposetrucks. The result is that the majority of trucks onthe road arent subject to underride rules.

Meanwhile, the passenger vehicle eet haschanged dramatical ly since NHTSA wrote the

standards. Regulators then were concerned thatoverly rigid guards could result in passengercompartment forces that would increase the riskof occupant injuries even in the absence of under-ride. The agency also recognized the need forbalancing energy absorption with guard strengthbecause the more the guard yields, the farther thecolliding vehicle travels and the greater likelihoodof passenger compartment intrusion.

The Institutes latest analysis indicates thatguards too weak to adequately mitigate underrideare a bigger problem than overly stiff guards.

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4 Status Repo rt, Vol. 46, No. 2, March 1, 2011

continued from p. 2)didnt involve und erride o r had only negligibleunderr ide, a nding in line with p rior stud ies.

Nearly half of the p assenger vehicles h ad un derride d amage classi-ed as severe or catastrop hic, meaning the entire front end or moreof the vehicle slid beneath the truck, resulting in loss of survival

space in the occup ant compar tment due to intrus ion. These vehiclesaccounted for 23 of the 28 crashes in which someone in the pas sen-ger vehicle died.

Many of the cas es of severe und erride involved trucks and tr ailersexempt from underride-related safety standards. More than half of the trucks in the study werent required to have guards, althoughmany had them anyway. The two largest exempt groups were trailerswith rear wheels set very close to th e back of the trailer and s traighttrucks (single-unit trucks with a cab and cargo body on on e chass is).Dump trucks represented a particularly hazardous category of straight truck. They accounted for about one-third of the straighttrucks b ut h alf of all the st raight t ruck crash es involving severe orcatastrophic underride.

When t railers did have regulation guards, researchers identied 3main failure modes. The most common reason was simply that theattachment between the guard and trailer was weak. This was thecase in wide overlap crashes (involving the center of the guard)when the attach ment between the guards vertical supp orts and trail-er chas sis broke where the guard was bo lted or welded to the trailer.Weakness also was a prob lem in narrow overlap crash es where a p as-senger vehicle struck one out board end of a guards main hor izontalbeam, causing it to bend forward or shear off completely. In thethird type of failure, an underride guard remained attached to itstrailer, but the trailer chassis itself buckled, causing the guard torotate up and forward.

The Institute didnt attempt t o compare th e performance of under-ride guards b uilt before and after th e 1996 release of upgraded fed-eral standard s regarding guard size, strength testing, and energy ab-sorption(see p.3). NHTSA recen tly did tr y to s ee if guard s complyingwith the r ules that took effect in 1998 reduce d eath and injury risk forpeople in pas senger vehicles. In a te chnical report p ublished in late2010, the agency said it couldnt identify a decline in underridedeaths, mainly because the Fatality Analysis Reporting Systemdoesn t record trailer model years and other d etails needed to d eter-mine whether a particular trailer was covered by the current rule.

Databases from North Carolina and Florida that contained modelyear information suggested there may have been an improvement,but th e number of crashe s was small and other det ails were missingso th e estimates were inconclusive.

Crash tests: The Institutes st udy raised q uestions ab out h ow andwhy guards failed, so researchers followed up with a series of 6 crashtests evaluating 3 semi-trailer rear guards complying with US rules.Two of the trailers also are cer tied to Canadian requirements, whichare more str ingent than the United States when it comes to st rengthand energy absorp tion. The tests involved cras hing a 2010 ChevroletMalibu into the rear of parked trailers.

h n evr let Malibu, a SAF TY PIC struck the back f aHyundai trailer (top) in he full-width test at 35 m h, damage wasso severe that people ina real crash likethis test wou d have died.

The underride guard bentforward, shearing its attachment boltsand pulling away from the trailer. This was the weakest under

uard the Institute evaluated. In on sh t ers s u l p t e r rom underriding the

trailer. The Wabash was the strongest of the 3 underride guards the Institute evaluated.

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Status Rep ort, Vol. 46, No. 2, March 1, 2011

The goal wasnt to evaluate th e Malibuworthiness. The m idsize sed an is an InstTOPSAFETY PICK and earns a 5-star safety ratiNHTSAs New Car Assessment Program.

The aim was to see if some un derride

perform better than others and to identcrash speeds and congurations producent types of failure, Lund says. Damacars in some of these tests was so devthat its h ard to watch th e footage withoing. If these had been real-world crashwould be no sur vivors.

Decapitation is a threat in underride cr3 of the crash tests the heads of the dumthe und erriding car made contact with eintruding trailer or the cars hood after itand push ed into the occupant compartmsuch test involved a Hyundai trailer whoride guard bent forward, sheared its attbolts, and b roke after the Malibu hit it in trear at 35 mph. This was the weakest guaThe trailer was manufactured by Hyundlead, a San Diego, Calif.-based subsidiaryKorea s Hyund ai Motor Co.

In contrast, a Wabash trailer outttedguard certied to Canadian specicaticessfully prevented und erride of the Malsenger compartment in a center-rear temph. The trailer was manufactured by LInd.-based Wabash National Corp. Its guthe s trongest of the 3 evaluated.

Its clear to our en gineers that Wabashstands how underride guards and trailetogether as a unit instead of treating themarate components, Lund says. Strongments kept the Wabash guard in place soengage the Malibu, allowing the ca rs st rabsorb and manage the crash energy. Inworld, this would be a s urvivable cras h.

Overlap tests are more challenging: To nd

out what h appens when a car hits th e traonly part of its front instead of head-on, tute ran offset tests with overlaps of 50and 30 percent. When the Institute evalusenger vehicles in its frontal crashworth igram, it uses a 40 percent overlap test at

In a 25 mph t est with a 50 percent o veguard on a Vanguard trailer tore away, amoderate underride. At 35 mph with thoverlap the underride was severe. The trmanufactured by Vanguard National Traile

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6 Status Repo rt, Vol. 46, No. 2, March 1, 2011

Monon, Ind.-based subsidiary of China Interna tional Ma-rine Containers Ltd. The guard is cer tied to US and Ca-nadian standards.

After the Wabashs good performance in the full-widthtest, engineers had high hopes for the offset tests. The

guard succes sfully prevented under ride in the test wherethe Vanguard failed (50 percent overlap at 35 mph ), eventhough the struck end s tarted to b end forward. The out-come for the Wabash was d ifferent when the overlap wasreduced to 30 percent. The struck end of the guard againbent forward, and this time there was s evere underride.

his test sh ows that even th e strongest guard left asmuch as half of the rear of the trailer vulnerable to se-vere underride. The guard only worked as intendedwhen the striking car engaged the center.

The best underride guard was a big improvementover the weakest one, but it still failed when hit near th eoutermost end of the guard, Lund says. Failures likethis were among the most common in our analysis of real-world crashes. Canadas underride standard istougher th an US requirements but st ill not strong enoughor comprehensive enough to prevent underride in crashcongurations t hat cau se many s evere injuries.

ffset tests stress guards unsupported outboardends. The vertical frame sup port s that attach guards totheir trailer chassis are located closer to guards cen-ters th an ends . Preventing underride in narrow overlapcrashes like these might mean devising a new way of

attaching guards t o trailers to utilize th e side r ails, inaddition to requiring manufacturers to cond uct comp li-ance tests with guards on tr ailers.

Under current certication standards, the trailer,underride guard, bolts, and welding dont have to betested as a whole system, Lund points o ut. Thats abig part of the problem. Some manufacturers do testguards on the trailer. We think all guards should beevaluated this way. At the least, all rear guards shouldbe as strong as the best one we tested.

Another problem is that regulatory gaps allow manyheavy trucks to forgo guards altogether. When they are

present on exempt trucks, guards dont have to meet1996 rules for s trength or energy absorp tion.

Under ride stand ards havent kept pace with improve-ments in passenger vehicle crashworthiness, Lundsays. Absent regulation, theres little incentive for man-ufacturers to improve underride countermeasures, sowe hope NHTSA will move quickly on our petition.

or a copy of Evaluation of US rear underride guardregulation for large trucks using real-world crashes byM.L. Brumbelow and L. Blanar, email publications@iihs.org.

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Status Report, Vol. 46, No. 2, March 1, 2011 7

LAURA P. SULLIVAN FORMER INSTITUTE CHAIRMALaura P. Sullivan, the on ly woman to se rve as chairman of the Insof director s, died Dec. 10, 2010, in Chicago. She was 63 years old

ullivan was vice pres ident, corporat e secretar y, and co unsel ountil her ret irement at the end of 2004. An Iowa native, she joined a senior at torne y in 1975. Before that, she was director o f the p rcasualty division of the Iowa Insurance Departmen t.

Sullivan se rved on th e Institutes board from 1984 to 1997 and 2002 to 2004. She was chairman d uring 1987-88.

MORE PEOPLE BUCKLE UP AMID HIGHER FINES FOR VIOLATIONS New research sponsored by the National Highway Trafc Safety

shows that increasing nes for violating safety belt laws can boost study by Bedford Research and the Pacic Institute for Research conrms that changing safety belt laws from second ary to primarymost effective in encouraging people to buckle up. But steeper negains in belt use, beyond what primary laws alone can accomplish, t

The author s found th at upgrading from a s econdar y to a p rimallows po lice to stop a driver on the b asis of that violation alone, seat belt use by 10 to 12 percentage p oints. Thats in line with p reabout th e importance of primary laws (seeStatus Report , Jan. 31, 2005, and A3, 2010; on the web at iihs.org).

When the res earchers looked at what happ ens when nes are ithe national median of $25 to $60, they found gains of 3 to 4 perRaising nes to $100 increases belt use by 6 to 7 percentage po in

The researchers calculated thes e increases using data from antional surveys in each state. They obtained similar results whesame ana lysis using a national crash datab ase with information fatally injured front-seat occupants.

The news that bigger nes lead to higher compliance gives stoo l for tackling a difcult prob lem. As the stu dys author s not e, ty belt use h as been a slow process in the United States. In 2010, percent far higher th an a few decades ago but lower than in mcountries, Australia, and Canada. US belt use varies widely amon68 percent in 2009 in Wyoming to 98 percen t in Michigan.

Despite safety belts impor tance in reduc ing injuries, nes gencompared with other trafc violations. Only New Mexico and thelumbia assess points against d rivers licenses when ad ults arent

The solution isnt just to make penalties as stiff as possible. As thpolice are unlikely to enforce laws if they believe the penalties arewhen it comes to belt violations theres room for harsher consequsurveys have found that nes of as much as $50 would enjoy brothough accep tance of penalty points for violations is much lower, th

Strategies to increase s eat belt us e: an analysis of levels of neof law by J.L. Nichols et al., is available at www.nhtsa.gov.

Vanguard trailer, 35 mph test, 50 percent overlap;

SEVERE UNDERRID ue to failed attachmentsconnecting the underride guard to the trailer.

Wabash trailer, 35 mph test, 50 percent overlap;NOUNDERRID ven though the struck end of theguard bent forward.

Wabash trailer, 35 mph test, 30 percent overlap;SEVERE UNDERRID as the struck end bent forward.

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1005 N. Glebe Rd., Arlington, VA 22201Phone 703/247-1500 Fax 247-1588Internet: www.iihs .orgVol. 46, No. 2, March 1, 2011

Underride guards can failin real-worldcrashes, and crash tests demonstratethe need for new standards to addressthe dead ly problem ...............................1

Moves to upgrade standardson under-ride guards have been slow coming ....3

Belt use riseswhen nes for not buck-ling up are increased .............................7

Laura P. Sullivanwas the rst womanto s erve as Institute chairman .............7

Contents may be republished with attribution.This publication is printed on recycled paper.

The Insuran ce Institute for Highway Safety is anonprot scientic and educational organizationdedicated to reducing deaths, injuries, and propertydamage from crashes on the nations highways.The Institute is wholly supported by auto insurers:

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